You are correct with your argument that China needs to help Afghanistan to grow out of poverty. That would be a great showcase of China as an alternative partner to work with.I would respectfully disagree.
No pain, no gain. China is now handed a golden piece of real estate on a silver plate, and given a real opportunity to showcase its meritocracy and strength in governance to the global south. What better platform to show its admirable strengths to the entire world by working with the Taliban and building up Afghanistan? well, nobody expects China can transform A-stan into another China, but at least a semblance of progress can be made? Besides, I feel that the Taliban is sincere in asking China for help, and if China sticks to development projects only, and not interfere with the political process in the country, there should be less opposition to its presence in A-stan. If China waits until all is rosy and good in its neighbour, the opportunity to help may never come. Time for China to stand up and be counted as a strong and reliable force for development and progress in contrary to the US.
If A-stan remains unstable and poor, it will remain a haven for terrorists, which simply cannot be good for Xinjiang too.
so it is in China's interest and benefit to lend a helping hand when the new regime is still groping its way in its infancy.
the Bagram Base is a useful foothold for China.
just my 2 cents of humble opinion.
About the PLAAF using Bagram Air Base. Perhaps if that were to happen. The best way I can think off is that it should only be on the official invitation by the Taliban govt. Like the case of with Russia and the Khmeimim Air Base in Syria. And that should only be a last resort. Perhaps only when there is a scenario of mass-scale foreign-sponsored terrorism that could topple the Taliban govt, and plunge Afghanistan into a terrorist hellhole ISIL state like what was attempted in Syria. Such a thing could inevitably threaten China, Pakistan, and Central Asia. Only in that case, then military intervention looks somewhat justifiable. Better for China to also get the other stakeholders involved like Pakistan and Russia. But they all need to be careful about overstaying there.
But, if Afghanistan is in no imminent danger of plunging into an ISIL state. Then its better for China to keep military options off the table. My ideal scenario would be to have the Taliban invite Chinese contractors to renovate Bagram Air Base into a civilian airport complete with a NATO atrocity museum. That would reinforce the idea that China is there to bring about positive progress. And with an added bonus of also becoming an embarrassment for those NATO imperialist powers.